1. Field of Invention
The present invention relates to a contact terminal used for the purpose of making electrical connection for connection to a power source, or inspection of a printed circuit board, an electronic component or the like. Particularly, the present invention relates to a contact terminal enabling a relatively large current to flow.
2. Description of the Background Art
A contact terminal used for connection to a power source, or inspection of a printed circuit board, an electronic component or the like is a component for obtaining electrical connection while making one end portion of the contact terminal contact with a terminal on a board. According to many types of contact terminals, a coil spring is inserted into an elongate hole provided in a metal-made main body case, a plunger pin is then inserted into the elongate hole, and only a front end portion of the plunger pin is maintained to protrude from the main body case. When this front end portion and the main body case are together pressed against a target position (e.g., a contact point or the like of a printed circuit board or the like) for obtaining electrical connection, the plunger pin slides along the elongate hole of the main body to move backward relative to the main body. In other words, while the plunger pin moves toward an inner side of the elongate hole, electrical connection between the contact point and the plunger pin can be made. As a result, a current flows from the contact point or the like via the plunger pin to the main body case.
By the way, when a relatively large current flows from the contact point or the like via the plunger pin to the main body case, if a current flows also in the coil spring, the coil spring can be burned out by heating due to electrical resistance. For example, when a part of a current flows in the coil spring, from a state where turning parts of the compressed coil spring contact with one another at side surfaces thereof, restoring of the coil spring causes the turning parts to be separated from one another to decrease a sectional area of a current path. As a result, electrical resistance rapidly increases, and the spring coil is thereby heated excessively to be burned out. For this reason, a contact terminal provided with a mechanism for preventing a current from flowing in a coil spring has been developed.
For example, Japanese Patent Application Laid-Open Publication No. 1994-61321 discloses a contact probe that is a contact terminal in which a small diameter portion whose diameter is reduced from a plunger pin is provided at a part of the plunger pin along a longitudinal direction thereof, a protrusion of a main body is made to enter a space of the small diameter portion to prevent the plunger from falling out of an elongate hole of the main body, and an insulation ball is arranged between the plunger pin and a coil spring. Since the insulation ball insulates the coil spring from the plunger pin, a current can flow from the plunger pin to a main body case while a current does not flow in the spring coil. Further, an end portion of the plunger pin positioned inside the elongate hole forms an oblique surface thereon. Thereby, the insulation ball can cause the plunger pin to be pressed against the inner surface of the elongate hole of the main body case. Accordingly, a current can reliably flow from the plunger pin to the main body case.
Further, Japanese Utility Model Application Laid-Open Publication No. 1995-34375 discloses a contact probe that is a contact terminal in which a plunger pin that includes a tip end part having a reduced diameter is inserted into an elongate hole of a main body, and a diameter of an opening of the elongate hole is reduced. Thereby, only the tip end part protrudes from the opening. Thus, the plunger pin is prevented from falling out of the elongate hole of the main body case. Furthermore, in this contact terminal, a conductive ball as well as an insulation ball such as the ball disclosed in the first-mentioned publication are arranged between the plunger pin and the coil spring. The insulation ball insulates the coil spring from the plunger pin. Meanwhile, the conductive ball presses the plunger pin against the main body case. Further, the conductive ball functions as a conductive path between the plunger pin and the main body case. With such a configuration, a current does not flow in the coil spring, and a current can reliably flow from the plunger pin to the main body case.
When a diameter (width) of a contact terminal is increased to increase a sectional area of a current path, a current quantity passing a unit area can be decreased. As a result, a quantity of a current flowing in a coil spring can be decreased. However, for an electric device that does not use a connector, and uses a contact terminal, a smaller size of the contact terminal is generally demanded, and terminals and contact points are arranged on a printed circuit board or the like in high density. To make it possible to use a contact terminal so as to satisfy these demands of such various types of devices, it is not desirable to increase a diameter (width) of the contact terminal to increase the sectional area.
The present invention was made in view of the above-described circumstances, and an object of the present invention is to provide a contact terminal that enables a relatively large current to flow therethrough.